Commit 23959281 authored by Rokudo Yan's avatar Rokudo Yan Committed by Linus Torvalds
Browse files

zsmalloc: account the number of compacted pages correctly 

There exists multiple path may do zram compaction concurrently.
1. auto-compaction triggered during memory reclaim
2. userspace utils write zram<id>/compaction node

So, multiple threads may call zs_shrinker_scan/zs_compact concurrently.
But pages_compacted is a per zsmalloc pool variable and modification
of the variable is not serialized(through under class->lock).
There are two issues here:
1. the pages_compacted may not equal to total number of pages
freed(due to concurrently add).
2. zs_shrinker_scan may not return the correct number of pages
freed(issued by current shrinker).

The fix is simple:
1. account the number of pages freed in zs_compact locally.
2. use actomic variable pages_compacted to accumulate total number.

Link: https://lkml.kernel.org/r/20210202122235.26885-1-wu-yan@tcl.com


Fixes: 860c707d ("zsmalloc: account the number of compacted pages")
Signed-off-by: default avatarRokudo Yan <wu-yan@tcl.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent f0231305

drivers/block/zram/zram_drv.c

+1 −1
Original line number Diff line number Diff line
@@ -1081,7 +1081,7 @@ static ssize_t mm_stat_show(struct device *dev, 
			zram->limit_pages << PAGE_SHIFT,

			max_used << PAGE_SHIFT,

			(u64)atomic64_read(&zram->stats.same_pages),

			pool_stats.pages_compacted,

			atomic_long_read(&pool_stats.pages_compacted),

			(u64)atomic64_read(&zram->stats.huge_pages),

			(u64)atomic64_read(&zram->stats.huge_pages_since));

	up_read(&zram->init_lock);

include/linux/zsmalloc.h

+1 −1
Original line number Diff line number Diff line
@@ -35,7 +35,7 @@ enum zs_mapmode { 


struct zs_pool_stats {

	/* How many pages were migrated (freed) */

	unsigned long pages_compacted;

	atomic_long_t pages_compacted;

};



struct zs_pool;

mm/zsmalloc.c

+11 −6
Original line number Diff line number Diff line
@@ -2212,11 +2212,13 @@ static unsigned long zs_can_compact(struct size_class *class) 
	return obj_wasted * class->pages_per_zspage;

}



static void __zs_compact(struct zs_pool *pool, struct size_class *class)

static unsigned long __zs_compact(struct zs_pool *pool,

				  struct size_class *class)

{

	struct zs_compact_control cc;

	struct zspage *src_zspage;

	struct zspage *dst_zspage = NULL;

	unsigned long pages_freed = 0;



	spin_lock(&class->lock);

	while ((src_zspage = isolate_zspage(class, true))) {
@@ -2246,7 +2248,7 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class) 
		putback_zspage(class, dst_zspage);

		if (putback_zspage(class, src_zspage) == ZS_EMPTY) {

			free_zspage(pool, class, src_zspage);

			pool->stats.pages_compacted += class->pages_per_zspage;

			pages_freed += class->pages_per_zspage;

		}

		spin_unlock(&class->lock);

		cond_resched();
@@ -2257,12 +2259,15 @@ static void __zs_compact(struct zs_pool *pool, struct size_class *class) 
		putback_zspage(class, src_zspage);



	spin_unlock(&class->lock);



	return pages_freed;

}



unsigned long zs_compact(struct zs_pool *pool)

{

	int i;

	struct size_class *class;

	unsigned long pages_freed = 0;



	for (i = ZS_SIZE_CLASSES - 1; i >= 0; i--) {

		class = pool->size_class[i];
@@ -2270,10 +2275,11 @@ unsigned long zs_compact(struct zs_pool *pool) 
			continue;

		if (class->index != i)

			continue;

		__zs_compact(pool, class);

		pages_freed += __zs_compact(pool, class);

	}

	atomic_long_add(pages_freed, &pool->stats.pages_compacted);



	return pool->stats.pages_compacted;

	return pages_freed;

}

EXPORT_SYMBOL_GPL(zs_compact);
@@ -2290,13 +2296,12 @@ static unsigned long zs_shrinker_scan(struct shrinker *shrinker, 
	struct zs_pool *pool = container_of(shrinker, struct zs_pool,

			shrinker);



	pages_freed = pool->stats.pages_compacted;

	/*

	 * Compact classes and calculate compaction delta.

	 * Can run concurrently with a manually triggered

	 * (by user) compaction.

	 */

	pages_freed = zs_compact(pool) - pages_freed;

	pages_freed = zs_compact(pool);



	return pages_freed ? pages_freed : SHRINK_STOP;

}